Radiation protection at synchrotron radiation facilities

A synchrotron radiation (SR) facility typically consists of an injector, a storage ring, and SR beamlines. The latter two features are unique to SR facilities, when compared to other types of accelerator facilities. The SR facilities have the characteristics of low injection beam power, but high stored beam power. The storage ring is generally above ground with people occupying the experimental floor around a normally thin concrete ring wall. This paper addresses the radiation issues, in particular the shielding design, associated with the storage ring and SR beamlines. Normal and abnormal beam losses for injection and stored beams, as well as typical storage ring operation, are described. Ring shielding design for photons and neutrons from beam losses in the ring is discussed. Radiation safety issues and shielding design for SR beamlines, considering gas bremsstrahlung and synchrotron radiation, are reviewed. Radiation source terms and the methodologies for shielding calculations are presented.     

Superheated drop neutron detectors used at the ESRF

The ESRF operates a 6 GeV electron storage ring to produce X-rays. The experimental hall is classified as a free access area in terms of radiation protection. Interlocked radiation monitors guarantee the corresponding dose constraint. Measurements have shown that the radiation field outside the storage ring is dominated by neutrons. Apfel REMbrandt superheated drop detectors have been chosen. In total, 64 monitors are installed around the storage ring, interlocked to the accelerator personnel safety system. Since the radiation fields are highly pulsed, the response of the REMbrandt monitors to pulsed radiation was measured and compared with theoretical predictions. Dose recordings from the bubble detectors are shown, illustrating the good correlation between beam losses and dose rates, as well as showing the correspondence between neutron and photon dose values. Finally, around the beamline hutches, REMbrandt neutron monitors have been used to evaluate the ratio between neutron and photon dose rates.     

Failure Analysis of Swelling in Prismatic Lithium-Ion Batteries During Their Cycle Life After Long-Term Storage

This paper details the failure analysis of swelling in prismatic lithium-ion batteries (LIBs) after undergoing several charge–recharge cycles subsequent to long-term storage. The methods of analysis are nondestructive and mainly involve the use of computed tomography (CT) and cell disassembly. Two situations are compared. The first cell is examined after long-term storage, in which case a void space, presumably a gas bubble, is observed around the Ni tap in the cell, and traces of side reactants are found around the center of the anode electrode. This cell is compared with a swollen cell examined after undergoing several cycles after long-term storage, in which, according to the CT results before and after gas removal, gas is detected inside the jelly roll and inside the space between the can body and the jelly roll. Moreover, side reactants are identified near the center of the anode electrode, causing the color of the anode electrode to become irregular. The results show the gas bubbles and side reactants generated as a result of long-term storage are determined to be responsible for the swelling in the cell due to prolonged cycling.     

Absorbed doses due to synchrotron radiation in the tunnel of the storage ring petra

Absorbed doses due to synchrotron radiation were measured in the accelerator tunnel of the high-energy electron-positron storage ring PETRA, at beam energies between 17 and 22.8 GeV. For energies between 17 and 30 GeV calculations were performed using the Monte Carlo code EGS. An agreement with the measured values was obtained within a factor of 2. In addition, the absorbed doses in a straight part of the accelerator tunnel were studied.     

Method for stabilizing beam intensity and energy in the SPring-8 linac

In any electron accelerator facilities, radio frequencies (RF) for a linear accelerator and a circular accelerator that includes a booster synchrotron ring and a storage ring are completely different. There is not necessarily a sub-harmonic relation of two RFs between a linear accelerator and a circular accelerator. It is, however, indispensable to obtain a synchronous relation between both RFs and the timing of the gun trigger signal with the increasing beam current and shortening of beam time width from an electron gun in a linear accelerator. For a synchronous timing system in any electron accelerator facilities, there is no choice but to assemble a complicated system with the frequency dividers and multipliers in order to realize the synchronous relation between both RFs and the gun trigger signal. To simplify the complicated synchronous timing system, we have developed a new synchronization method for the RFs of both linear and circular accelerators. The new synchronization system has been installed into the synchrotron radiation facility, SPring-8 (Super Photon ring 8 GeV), which consists of a 1-GeV linac, an 8-GeV booster synchrotron and an 8-GeV storage ring. A 2856 MHz RF for the 1-GeV linac was generated by the 508.58 MHz RF of the 8-GeV storage ring with the new synchronous timing system, and the emission and acceleration under the condition of the shortening the beam time width in the linac was carried out. Since the synchronous relation between both the RFs and the gun trigger signal was realized by using the new synchronous timing system, the time jitter between the gun trigger signal and the RF phase of 2856 MHz was significantly reduced and resulted in beam energy stabilization. The new synchronous timing system has been used for usual beam operations at SPring-8. This timing system has achieved time jitters of 3.5 ps (rms) and beam energy stability of 0.009% (rms) under the condition of completely synchronized two RFs and the gun trigger signal.     

光电技术在合肥光源束测量系统中的应用

介绍了光电技术在合肥同步辐射加速器束流测量系统中的应用。介绍了合肥 2 0 0 Me V电子直线加速器利用光电二极管阵列的能谱测量系统、合肥 80 0 Me V电子储存环利用 CCD技术的束流截面测量系统以及利用单光子计数法测量束团纵向精细结构。本文给出了测量结果。     

13 years’ operational experience of SPring-8 vacuum system

The first electron beam was stored in SPring-8 storage ring in March 1997. An overview of the 13 years’ operational experience concerning the vacuum system of the SPring-8 storage ring is presented. The evolution of the vacuum system and their performance are summarized. Moreover, the main vacuum failures and their impact on accelerator operation are described in detail. We analyze the relationship between the difference types of vacuum failure and downtime of user experiment.     

Development of SPring-8 vacuum system

SPring-8 storage ring has been available for user operation with low emittance and extreme stability for over 10 years. However there occurred some problems in the components of the storage ring due to high-brightness synchrotron radiation (SR) and low-emittance operation. On the vacuum system of the storage ring, an accurate pressure could not be measured near the photon absorber due to scattered high-energy SR to the gauge head. High-energy SR activated dissolved oxygen in cooling water, and the activated dissolved oxygen corroded the inside of the photon absorbers in SR irradiation part. Air leakage occurred at an injection chamber due to impact by a small-size electron beam produced by low-emittance operation.We investigated the cause of the aforementioned difficulties with the vacuum system and prescribed the treatments described in this paper. In addition, we are making continual efforts at further system upgrades such as developing an RF shield that suppresses temperature increase in the shield in possible high-current operation.     

The electron-proton colliding beam facility HERA

The HERA electron-proton storage ring now under construction at DESY will collide 30 GeV electrons with 820 GeV protons. The physics programme, the layout of the machine and the development of superconducting accelerator magnets are described.     

HLS储存环压强分布计算

在储存环中束流寿命与残气压强息息相关,而储存环真空系统的特殊结构又影响压强计算、测量的精确性,因此储存环压强的准确读取一直为人们所关注。本文主要介绍合肥光源(HLS)储存环真空系统压强分布的计算,将计算结果与实际运行数据比较,两者基本相符,因此该计算程序可用于预测、模拟环真空系统各种运行状态。     

Radiation safety survey on a flattening filter-free medical accelerator

Dose rates at several locations outside a treatment room were measured for 6 and 18 MV photon beams from a Varian Clinac 21EX accelerator operated with and without a flattening filter. Also, dose rates in the treatment room due to activation were measured at 18 MV. An analysis of the measured data is presented. The results suggest that substantial reduction in doses outside the treatment room and lower activation can be achieved with a flattening-filter free accelerator.     

Ergonomic workplace design in the fast pick area

The aging society in many developed countries has made an ergonomic workplace design to an important topic among researchers and practitioners alike. We investigate the workplace design for order pickers that manually collect items from the shelves of a warehouse. Specifically, we treat the storage assignment, i.e., the placement of products in shelves of different height, and zoning, i.e., the partitioning of the storage space into areas assigned to separate pickers, in the fast pick area of a warehouse. A fast pick area unifies the most fast-moving items in a compact area, so that workers are relieved from unproductive travel, but face extraordinary ergonomic risks due to the frequent repetition of picking operations. Concerning the health of (aged) workers, it is crucial to reduce such risks. Thus, we define a combined ergonomic storage assignment and zoning problem with the objective of minimizing the maximum ergonomic burden among all workers. This problem is formalized, and two construction heuristics and a tabu search procedure are proposed. Our results show that neglecting ergonomic aspects and only focusing on picking performance leads to much higher ergonomic risks of the workforce.

     

An active storage cell for a polarized gas internal target

The first experiment using an active storage cell for polarized atoms to increase the target thickness in an electron storage ring has been performed at the VEPP-3 facility. A clam-shell storage cell, which is opened while injecting electrons into the storage ring and closed during operation, was used to increase the target thickness viewed by the detector system. The average tensor polarization of the target was found to be p_zz = 0.59 ± 0.14 and the figure of merit was increased by more than a factor of thirty in comparison with a direct jet thickness. The measured target thickness and polarization are in a good agreement with the expected values.     

Radiation safety systems for accelerator facilities

The radiation safety system RSS) of an accelerator facility is used to protect people from prompt radiation hazards associated with accelerator operation. The RSS is a fully interlocked, engineered system with a combination of passive and active elements that are reliable, redundant and fail-safe. The RSS consists of the access control system (ACS) and the radiation containment system (RCS). The ACS is to keep people away from the dangerous radiation inside the shielding enclosure. The RCS limits and contains the beam/radiation conditions to protect people from the prompt radiation hazards outside the shielding enclosure in both normal and abnormal operations. The complexity of an RSS depends on the accelerator and its operation. as well as associated hazard conditions. The approaches of RSS among different facilities can be different. This report gives a review of the RSS for accelerator facilities.     

Charge capacity limitations of radio frequency ion guides in their use for improved ion accumulation and trapping in mass spectrometry

The use of radio frequency (rf) ion guides as "linear" two-dimensional ion traps and ion guides for ion storage and accumulation, respectively, is becoming increasingly important for realizing improved sensitivity in mass spectrometry. Analytical relationships describing the ion accumulation operation mode of rf ion guides are reported. Comparisons are made between the rf quadrupole ion guide, higher-order rf multipoles and rf stacked ring ion guides, in terms of the charge capacity limitations due to the instability of ions, rf focusing efficiency limits, and effects due to rf ion heating (i.e., collisional activation due to rf oscillations of ions). Analytical relations for the stored charge quantity are derived in the low ion energy approximation, which is shown to be reasonable for the systems considered. The ion density spatial distribution is derived, an exponential form of which proved to provide a good approximation for high-order rf multipoles and stacked ring rf ion guides. The limit on the stored charge dependence upon rf is shown to be directly related to the thermal dissociation thresholds for the ions being studied; the limitation is weaker for higher-order multipoles and stacked ring ion guides. These results suggest that rf quadrupoles provide an optimum configuration when accumulation of a moderate ion density is sufficient (below 10(9) elementary charges/m). Alternatively, accumulation of an appreciable density for more fragile species, such as noncovalent complexes, may be realized using higher-order multipoles and stacked ring ion guides.     

Acceleration strategy for compact storage rings with low energy injection scheme

The acceleration strategy for an accelerator with a low energy injection scheme (LEI) is investigated. The space charge octupole-like effect caused by the electron beam and trapped ions plays an important role in beam injection and acceleration. We present an acceleration method that makes it possible for Super-ALIS, a superconducting compact storage ring, to achieve a stored current of over 200 mA with injection at 15 MeV.     

Design and experiment results of the LEBT pre-chopper for CSNS

In a high intensity proton accelerator complex comprising a linac and a ring, a beam chopper is often necessary in order to reduce the beam loss during injection from the linac to the ring. The China Spallation Neutron Source (CSNS) front end incorporates a pre-chopper in the Low Energy Beam Transport line (LEBT) that will remove a 530 ns section of beam at approximately 1 MHz rate. Physical design of the pre-chopper is presented in this paper. The distinguished feature of this electrostatic beam chopper is the novel design of deflecting structure, and the theoretic fast beam rise/fall time, which is an essential requirement for CSNS accelerator to avoid radioactivity induced by the lost particles due to insufficient chopping during the transient time; Taking advantage of the existing LEBT of the Accelerator Driven Subcritical System (ADS), the beam study of a similar chopper system was successfully performed and the achieved rise/fall time was less than 20 ns, which is the fastest one compared to other similar pre-choppers. This type of pre-chopper will be used in the CSNS LEBT, which is under construction.     

200MeV直线加速器真空系统设计、安装及运行现状

介绍合肥国家同步辐射装置作为800MeV电于储存环的注入器，200MeV电子直线加速器真空系统的概况、工程计算和设计以及运行过程初期和3年来真空系统的变化，出现的故障及原因。     

Radiation issues in a radioactive ion decay ring

In a beta-beam facility, a pure beam of electron neutrinos, or their antiparticles, are produced by the decay of fully stripped radioactive ions (6He and 18Ne) circulating in a storage ring. Since the beam is not extracted from the ring, all the particles will eventually be lost somewhere in the machine and thus activate the accelerator components and the surrounding concrete and rock. In particular, as nuclei change their charge in beta-decay, a large part of the particles will be lost in the arcs of the decay ring and mainly irradiate the magnets. The density of inelastic interactions of hadrons in the magnets, concrete and rock and the track-length distribution of secondary hadrons were calculated by means of the FLUKA Monte Carlo code. These values were used to estimate the induced radioactivity in the facility, the dose rates expected in the decay ring and the consequences for the environment.